The present invention relates to a pump unit for supplying fuel, preferably diesel oil, to an internal combustion engine.
In particular, the present invention relates to a pump unit of the type comprising a high-pressure pump for supplying the fuel to the internal combustion engine and a pre-supply pump for supplying the fuel to the high-pressure pump.
Generally, the high-pressure pump comprises a pump body having a central bore and at least two lateral bores, which have respective longitudinal axes parallel to one another and perpendicular to a longitudinal axis of the central bore, and face toward this central bore.
Each lateral bore houses within it a tubular head comprising a constricted portion forming a cylinder of the high-pressure pump and a widened portion connected to the constricted portion at an annular shoulder.
The fuel is supplied into the cylinder through an intake valve, which comprises a valve body mounted in the widened portion in contact with the annular shoulder, and has a shutter member mounted through the valve body so as to move between an open and a closed position of the intake valve.
The head is closed axially by a plug screwed into the widened portion to lock the valve body axially against the annular shoulder.
Each head also has a conduit for supplying fuel to the widened portion of the head, and then to the intake valve, and houses within it a delivery valve for selectively controlling the supply of fuel to the internal combustion engine.
The cylinders are slidingly engaged by respective pistons which can move with a reciprocating rectilinear motion along the corresponding cylinders under the force imparted by a drive device, comprising a transmission shaft mounted rotatably through the aforesaid central bore of the pump body and, for each piston, a respective spring interposed between the head and the piston.
Each piston is moved by the corresponding spring in a stroke for the intake of fuel into the corresponding cylinder, and by the transmission shaft in a stroke for the delivery of the fuel from the corresponding cylinder to the internal combustion engine.
Since each head includes the structure of the corresponding supply conduit and the screw thread of the corresponding widened portion, known pump units of the type described above have a number of drawbacks, mainly due to the fact that the production cycle for the corresponding heads is relatively complex and costly.
Furthermore, because of the presence of a closing plug for each head, the pump units have a relatively large number of components and a relatively long assembly time, while, owing to the presence of the conduits for supplying fuel to the cylinders, the overall dimensions and weights of the heads are relatively high.